$1000 per head is a good budget. The rules are simple you buy a beater and can spend no more than 500 clams, all in, in performance. Remove all glass, add racing seat, harness, cage, battery cutout. Might as well remove all interior at this point. Safety items i just mentioned and brakes are not part of the budget, but again no need for much besides decent fluid since the car in front of you will help you stop anyway. If you cheat with engine, etc, they will add negative laps to you and get shamed, so not worth it, besides the track is too short for it. In the past we tried everything we could think of to cheat, even using "rust paint" on parts. The judges know all the tricks and fine you. The fines are lessened if you offer alcohol sacrifices during tech inspection.
At CMP they do not do the full track (2.5miles, 14 turns), they only use the front section. HP is useless as you may have 100 cars "racing" in less than a mile long track, its more like LA traffic at rush hour. Lots of door to door racing, paint scraping banging and more banging in the melee. A small reliable car works great, with good gas mileage to prevent pit stops for gas.
Lots of people camp at CMP, or bring motor homes, tons of space for it, but will be a loud party all night. So that can be cheap. It can be a memorable event! There seems to always be some "douche in a mustang" that gets the "curse of the people" award, and that car will be crushed by a large backhoe. Organizers reserve the right to buy any car entered for $500, another way to keep cheating down.